A Computational Method For The Fatigue Asessment Of Self-elevating Platform

Fatigue strength calculation is very necessary in the early design of self-elevating platform, a kind of important mobile platform. However, the existing fatigue algorithm each has its own advantages as well as shortages.For the simplified method, existing standards have not make a clear regulation of simplified formulae, making a few approximate treatment inevitable; Spectrum analysis request linear systems, therefore linearization is needed and the effect of power is ignored. For fatigue load calculation, wind load is calculated as the average load in most of the existing classification specifications.However, the actual wind load on structure is a random process,and the effect of fluctuating wind load on the strength and fatigue of self-elevating platform can not be considered in the above two methods.Based on this background, in this paper, firstly the fatigue strength of self-elevating platform was calculated by the spectral analysis method, furthermore, the fluctuating wind load of self-elevating platform is simulated and the nonlinear time domain method was put forward, taking the effect of dynamic effect and fluctuating wind-load into account.The main contents are as followed:(1) By the harmonic synthesis method, the fluctuating wind speed and fluctuating wind load of Self-elevating platform is simulated based on Davenport spectrum, and the time dependant fluctuating wind speed and fluctuating wind load is obtained, which can be used for dynamic analysis and fatigue analysis.(2) According to ABS guidance, the fatigue accumulating damage of self-elevating platform was calculated with spectrum analysis.(3) The dynamic response of self-elevating platform is discussed and the effect of dynamic and fluctuating wind load to the stress response is analyzed.(4) The fatigue accumulating damage of two conditions(both in irregular wave loads and combinations of random waves and winds) was calculated using nonlinear time domain method, through comparison of which the effect of fluctuating wind load on the fatigue strength of sef-elevating platform effects is obtained.